1. Field of the Invention
This invention relates to a method and apparatus for verifying a color of an LED in a printed circuit board.
2. Description of Related Art
Printed circuit boards often contain one or more light emitting diodes (LEDs) used as external signals, internal diagnostics and for other suitable applications. Typically, verification of the operation of a printed circuit board having LEDs required powering up a fully rendered printed circuit board and manually verifying the operation of the LEDs. Alternatively, a test fixture may be constructed including bulky and expensive fiber optics that extend between the printed circuit board to be tested and a test system.
A method and apparatus for verification of a color of an LED according to a preferred embodiment of this invention eliminates much of the time-consuming and costly procedures required by manual verification and the equally costly test fixtures having multiple and complex fiber optic runs.
The apparatus according to a preferred embodiment of this invention includes a sensor. The sensor preferably includes, in combination, a photosensitive semiconductor, an optical filter, a pair of probes and a bias resistor. The optical filter preferably permits only light from a target wavelength of the color to be detected from the LED to pass. The probes are connected with respect to the photosensitive semiconductor and the optical filter and pass current generated from the photosensitive semiconductor across the bias resistor. As a result of the described construction, the sensor provides an output voltage corresponding to a target wavelength corresponding to an appropriate color of the LED and blocks light outside of the target wavelength.
In addition, a test system is in communication with the sensor for converting the output voltage into a machine or operator-readable pass/fail signal. The test system may be an in-circuit tester in combination with software suitable for translating the output signal from the sensor into such a pass/fail signal. The test system may additionally include a verification module for determining whether the output voltage exceeds a predetermined minimum test voltage for the intensity of light of the target wavelength and/or a warning signal to indicate excessive ambient light between the sensor and the LED.
The software and/or the test system may be configured to include the steps of: (1) measuring a Von across the sensor when the LED is on; (2) measuring a Voff across the sensor when the LED is off; (3) subtracting the yoff from the Yon to determine a nominal voltage; and (4) comparing the nominal voltage with a predetermined minimum voltage for the color to be verified.
It is one object of this invention to provide a method and apparatus for accurately and inexpensively verifying a color of an LED.
It is another object of this invention to provide a method and apparatus for verifying a color of an LED in a printed circuit board without requiring a fully operational and powered printed circuit board.
It is yet another object of this invention to provide a method and apparatus for verifying a color of an LED wherein existing test fixtures can be adapted for use in connection with the apparatus.
It is still another object of this invention to provide a method and apparatus for verifying a color of an LED that does not require adjustment of potentiometers or placement of optical cables.
It is yet another object of this invention to provide a method and apparatus for verifying a color of an LED that can utilize a common return and thus use only a single wire per sensor plus one for the common return.